Position BinarySearch( List L, ElementType X ){
	int l = 1;
	int r = L->Last;
	while(l <= r){
		int mid = (l + r) / 2;
		if(L->Data[mid] == X){
			return mid;
		}else if(L->Data[mid] > X){
			r = mid-1;
		}else{
			l = mid+1;
		}
	}
	return NotFound;
}

